Magnetically modulated vacuum arc diode

ABSTRACT

A vacuum arc switching device having a stationary cathode, a stationary spaced concentric anode, an ignitor electrode spaced from the cathode and an annular magnetic field coil concentric with and spaced from the anode.

United States Patent [15] 3,696,264 Clark, Jr. et al. [451 Oct. 3, 1972 [54] MAGNETICALLY MODULATED [56] References Cited VACUUM ARC DI DE 0 UNITED STATES PATENTS [72] Inventors: Richard J. Clark, Jr., San Jose,

c m; Han-y veron, Acton, 3,248,603 4/1966 Howell et a1 ..313/198 X Alexander Gilmour David 3,014,109 12/1961 Burger ..200/144 B Lockwood, both of w n n 2,892,145 6/1959 Garshelis ..313/ 153 X 2,953,714 9/1960 Rostas ..313/158 X 2,750,555 6/1956 Kather et a1. ..313/157 X [731 Asslgnee= Cmlell Aeronautical Laboratory, 3,202,852 8/1965 Martinson ..313/197 x Inc., Buffalo, NY.

22 Filed; June 24 1970 Primary Examiner-Alfred L. Brody Attorney-Allen J. Jaffe [21] Appl. No.1 49,473

, [57] ABSTRACT [52] US. Cl. ..313/160, 313/162, 313/ 197, A vacuum are switching device having a Stationary 313/198 315/267 344 cathode, a stationary spaced concentric anode, an ig- [51] Int. Cl ..HOIJ 1/50 nitol. electrode spaced from the cathode and an annw [58] Field of Search ..200/144 A, 144 B; 313/157,

lar magnetic field coil concentric with and spaced from the anode.

6 Claims, 3 Drawing Figures ANODE 8+ MAGNETIC FIELD COIL o PULS E GENERATOR 34 O-MM. H

28 IGNITER 22 SCR;

CATHODE PATENTED B 3 97 ANODE MAGNETIC FIELD COIL PULSE GENERATOR SHEET 2 0F 2 o-MM. v28

IGNITER/ scR.

)i [rLOAD CATHODE L INVENTOR MAGNETICALLY MODULATED VACUUM ARC DIODE BACKGROUND OF THE INVENTION The present invention relates to high current and high voltage switching devices, and more particularly to a stationary vacuum arc diode or switch that is modulated or'controlled by an externally applied magnetic field.

There has long been a need for switching devices that are capable of operating at high voltages and modulating the flow of large currents, greater than those normally controlled by conventional triodes or transistors.

There are currently known mechanical switching devices that operate in a vacuum environment. These usually comprise a pair. of separable contacts or electrodes located within an evacuated chamber. Circuit interruption is initiated by physically moving one contact away from the other whereby an arc is established.

Since the vacuum environment is of high dielectric strength, the are generally cannot sustain itself and, after a time, it is extinguished and the circuit is broken. Attempts have been made to speed up the arc extinction process by the utilization of various magnetic field producing devices which cause the terminals of the arc to move at high speed along the surfaces of the electrodes. Such movement tends to reduce the amount of metallic vapors generated by the electrodes, which in turn enables the vacuum to recover its dielectric strength to reduce the possibility of reestablishment of the arc.

Since these devices are mechanical, requiring a physical separation of the electrodes, they are relatively slow and have limited useful lives.

SUMMARY OF THE INVENTION The foregoing, as well as other, disadvantages of the prior art devices are overcome according to the present invention which provides a switching device that is extremely fast, has a long life and is capable of operating at high voltages and modulating the flow of large currents.

The present invention provides a magnetically controlled vacuum are switching having stationary spaced electrodes in a vacuum environment, between which a conducting path is achieved by the establishment of -,a vacuum are which creates a conducting plasma between the electrodes. The conducting path or circuit is opened by the action of an externally controlled magnetic field which causes the current paths between the electrodes to be deflected causing the entire plasma to rotate forming a dense rotating electron sheath whereby the impedance across the electrodes is increased rapidly. Thus, the conduction current that can pass between the electrodes is reduced. When this conduction current is reduced to a level below the threshold current for the cathode electrode material, the vacuum arc will be extinguished. The time it takes to extinguish the arc and thereby open the circuit is on the order of 2 microseconds.

The vacuum are switching device according to the present invention can advantageously be applied wherever large blocks of power are required to be controlled such as in high-power radar modulators, highpower lasers, d-c power transmission or the like.

Basically, then, the present invention provides a magnetically controlled vacuum arc switch, comprising; a stationary cathode; a concentric stationary anode; the cathode and anode located in a vacuum environment; means for generating a vacuum are on said cathode creating a conducting path between the anode and cathode; and means concentric with the anode for developing a magnetic field for modulating or extinguishing the vacuum arc.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the presentinvention, reference should now be had to the following detailed description of the same, taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic pictorialrepresentation of the vacuum arc switching device with parts thereof broken DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, and, more particularly, to FIG. 1, the vacuum arc diode or switching device according to the present invention is schematically depicted as comprising two general sections; an anode section 10 and a cathode section 20. As shown the anode is of tubular substantially frusto-conical construction having sidewalls 12 that are slightly tapered and a hollow interior chamber 14. The cathode and anode may be formed of any suitable metal, such as copper.

The cathode section 20 is adapted to be supported with a major portion thereof projecting interiorly of anode chamber 14, concentric with and spaced from the anode sidewalls 12. As illustrated more clearly in FIG. 2, section 20 comprises an interior rod or wire cathode 22, surrounded by an insulating element 24 which is concentric with the cathode and provides an abutment surface 26 therefor. Insulator 24 may be aluminum oxide or a like material. Concentric and in surrounding contacting relation with insulating element 24 is a generally cylindrical ignitor electrode 28 having an end 30 that partially overlaps an end 32 of the insulator 24.

Mounted exteriorly of anode 12, spaced therefrom and concentric therewith is a field coil 34, used for the modulation and extinction of the are, as will become apparent hereinbelow.

The above described components are all suitable mounted in an evacuated or vacuum environment.

The operation of the switching device will be discussed with the aid of the circuit diagram shown in FIG. 3, which, as illustrated, comprises; a first silicon controlled rectifier or the like, SCR located between a source of potential and the ignitor 28; an external load circuit L across the cathode and anode to be controlled thereby; a second rectifier SCR in series with the magnetic field coil 34 and a pulse forming network or generator, PFN, to be controlled by SCR When SCR,, is triggered on, a negative ignition pulse is generated, a portion of the energy of which is dissipated on the surface of cathode 22 by an electrical discharge across the end surface 32 of insulator 24. A

plasma cloud between cathode 22 and anode 10 is formed by cathode material which is evaporated during the ignition discharge. If the impedance and voltage of 5 established on the cathode and a conduction path to the anode will be maintained by the continued evaporation of the cathode material. Because there is no appreciable anode fall voltage in a vacuum arc, and because the voltage drop in the metallic plasma is extremely small, (about 0.01 volts per centimeter) the voltage appearing across the switch during fall conduction is essentially the cathode fall potential. This varies from metal to metal and is typically between l0 and 20 volts.

To modulate or extinguish the arc, and thereby open the circuit, SCR is triggered applying a coaxial magnetic field from coil 34 to the switch, whereby a plasma configuration is established similar to that which exists in a single-ended Penning discharge. As the magnetic field is applied the current paths between the anode and cathode are deflected, causing the entire plasma to rotate and also forminga dense, rotating electron sheath adjacent the anode. The combined effect of causing the plasma to rotateand of creating the extremely dense electron sheath at the anode is to increase the impedance of the switch by a very large factor, thereby reducing the current that can be passed.

When this conduction current drops to a level below the threshold current for the cathode material, then the arc will be extinguished.

With the above described apparatus voltages up to 3,000 volts and currents up to several hundred amperes have been achieved; and the shut-off time has been on the order of 2 X seconds.

Although a preferred embodiment of the present invention has been described, modifications will occur to those skilled in the art. It is therefore intended that the present invention is to be limited only by the scope of the appended claims. What is claimed is: 1. A vacuum are switching device, comprising; a. a stationary cathode, b. a concentric stationary anode, c. said cathode and anode being located in a vacuum environment,

d. means for generating a vacuum are on said' cathode creating a conducting path between said anode and cathode, and

.means concentric to said anode for developing a magnetic field for increasing the impedance across said anode and cathode to thereby extinguish said arc.

2. The switching device according to claim 1,

wherein;

f. said means for generating said vacuum arc comprises an ignitor electrode 'spaced. from said cathode, and

g. an insulator between said ignitor electrode and said cathode.

3. The switching device according to claim 2,

wherein h. (1 means concentric to said anode comprises an annular magnetic field coil. 4. The switching device according to claim 3,

' wherein;

i. said cathode comprise a cylindrical metallic rod,

and

j. said'anode comprises a substantially frusto-conical annular shell spaced from and in surrounding relation with said cathode.

5. The switching device according to claim 1,

wherein;

f. said means concentric to said anode comprises an annular magnetic field coil. 6. The switching device according to claim 5, wherein;

g. said cathode comprise a cylindrical metallic rod,

and h. said anode comprises a substantially frusto-conical annular shell spaced from and in surrounding relation with said cathode. 

1. A vacuum arc switching device, comprising; a. a stationary cathode, b. a concentric stationary anode, c. said cathode and anode being located in a vacuum environment, d. means for generating a vacuum arc on said cathode creating a conducting path between said anode and cathode, and e. means concentric to said anode for developing a magnetic field for increasing the impedance across said anode and cathode to thereby extinguish said arc.
 2. The switching device according to claim 1, wherein; f. said means for generating said vacuum arc comprises an ignitor electrode spaced from said cathode, and g. an insulator between said ignitor electrode and said cathode.
 3. The switching device according to claim 2, wherein; h. said means concentric to said anode comprises an annular magnetic field coil.
 4. The switching device according to claim 3, wherein; i. said cathode comprise a cylindrical metallic rod, and j. said anode comprises a substantially frusto-conical annular shell spaced from and in surrounding relation with said cathode.
 5. The switching device according to claim 1, wherein; f. said means concentric to said anode comprises an annular magnetic field coil.
 6. The switching device according to claim 5, wherein; g. said cathode comprise a cylindrical metallic rod, and h. said anode comprises a substantially frusto-conical annular shell spaced from and in surrounding relation with said cathode. 